1. Field of the Invention
The present invention pertains to methods and procedures for abandoning underground storage tanks, particularly those which contain or have contained hydrocarbon substances or any other substances of an environmentally hazardous nature.
2. Description of the Prior Art
There are thousands and probably millions of underground storage tanks in which gasoline, fuel oil or other hydrocarbons have been stored. The Environmental Protection Agency indicates that it is aware of at least five million underground fuel tanks in the United States of which an estimated thirty percent leak. Even though large numbers of these tanks may have been abandoned, many of them leak or have leaked residual substances into the surrounding soil. Others may not have yet leaked but will do so in the future. All of such underground storage tanks are potential pollution problems, polluting the surrounding soil and possible water sources. Federal and state agencies are now requiring that these tanks be removed or cleaned up and abandoned in some environmentally safe method.
Abandoned underground storage tanks also create many other related problems. Due to the potential liability from environmental pollution, the owners of property on which underground storage tanks may be situated are frequently prevented from transfer or sale of the property for several reasons. First and foremost, potential buyers do not want to assume the risk associated with abandoned underground storage tanks. Secondly, banks and other lending institutions may not be willing to loan money to the owner or purchaser of businesses, such as service stations, garages, etc., where underground storage tanks are involved. Some court decisions have held lenders liable for cleanup costs if they had foreclosed on contaminated property or had merely advised businesses that owned contaminated land. Lending institutions are thus reluctant to expose themselves to such potentially costly problems.
Because of the risks associated with underground storage tanks, new measures are being taken in new installations for detecting and preventing leaking underground storage. In some cases tanks are being placed above ground. However, this does not solve the problem of leaking tanks already in place.
The abandonment of subterranean cavities, such as abandoned mines, has long been of concern. U.S. Pat. No. 1,404,112 discloses a method of filling a subterranean cavity in which a slurry of soil and water is pumped into the cavity behind a temporary wall. The water is allowed to leak through the temporary wall, the soil remaining in position within the cavity. U.S. Pat. No. 3,892,442 discloses a more recent mining approach to this problem in which a foam material is dispensed in a mining shaft to fill the void created by removal of the mined product. Materials mentioned are polystyrene, polyurethane, foam cement, foam plastic, etc. Appropriate additives make the foam fire retardant.
The most widely utilized and accepted method of abandoning underground storage tanks at the present time is removal of the tanks. However, this is a very expensive, time consuming and business interrupting procedure. If any residual fluids are in the tank, they must be pumped out and disposed of in an acceptable manner. Heavy equipment must be brought in to remove soil surrounding the tank and the tank itself. If the surrounding soil is contaminated, the contaminated soil must be removed, temporarily contained and eventually disposed of in a manner acceptable to environmental pollution agencies. While waiting for disposal, the contaminated soil, due to vaporization of the contaminating substances therein, may pose health problems to the surrounding area. Then the cavity resulting from removal of the tank and/or the surrounding soil must be filled with uncontaminated soil. Such an operation may require days or even weeks and may be very destructive to other improvements of the subject property such as driveways, sidewalks, etc. It is most likely that such operations will also disrupt or totally suspend business operations of the business on whose property the tanks are disposed. It can be seen that this creates major problems.
Of course, the costly and disruptive procedure of removing an abandoned underground storage tank could be avoided if an acceptable method were found to abandon these tanks in place. One such method is proposed in U.S. Pat. No. 4,693,284 in which an abandoned underground storage tank is filled with a rigid polyurethane foam. The method revealed therein suggests removing any residual substances and evacuation and/or evaporation of vapors therefrom by forced air ventilation. It is suggested that prior to filling the tank with foam, minor amounts of solid absorbent materials be place in the tank to absorb condensation, water, mud, or sludge that might be left in the tank. It is not known whether this procedure has been approved by the various environmental pollution agencies. It is suggested in the patent that it might become necessary in the future to remove the tank as a result of regulatory requirements and that if the tank is removed it would be easier to handle filled with foam than not. Even if this procedure is approved and the tank never removed from the ground, a large mass of plastic foam is left in place, rendering a certain area of the property less usable for things such as structural support, water drainage, certain types of landscaping, etc. For example, the compressive strength of polyurethane is approximately 30 psi, substantially less than soil which is usually around 45 psi. Furthermore, filling a tank with polyurethane foam is relatively expensive and would be subject to exothermic reactions of 200 degrees F. or more, creating potential explosion hazards.
On the other hand, if the tank is filled with cement, the compressive strength is usually not less than 1500 psi. This creates a problem if, for any reason, future activities require digging a hole or trench through the tank fill material. Furthermore, it is almost impossible to completely fill a tank with cement since the cement does not flow easily into the tank.
As can be understood, the abandonment of underground storage tanks, particularly those in which hydrocarbon materials or their hazardous substances have been stored, has become a major problem. Efforts continue to be made to solve this problem in a safe, cost effective and environmentally accepted manner. Further improvements are needed.